diff --git a/reference/url/functions/parse-url.xml b/reference/url/functions/parse-url.xml
index b8f378e9cb..8ffc12ad5a 100644
--- a/reference/url/functions/parse-url.xml
+++ b/reference/url/functions/parse-url.xml
@@ -252,11 +252,15 @@ array(3) {
 
  <refsect1 role="notes">
   &reftitle.notes;
-  <note>
+  <caution>
    <para>
-    This function may not give correct results for relative URLs.
+    This function may not give correct results for relative or invalid URLs,
+    and the results may not even match common behavior of HTTP clients.
+    If URLs from untrusted input need to be parsed, extra validation is
+    required, e.g. by using <function>filter_var</function> with the
+    <constant>FILTER_VALIDATE_URL</constant> filter.
    </para>
-  </note>
+  </caution>
   <note>
    <para>
     This function is intended specifically for the purpose of parsing URLs